Economic importance Cumulate rock

1 economic importance

1.1 silicate mineral cumulates
1.2 oxide mineral cumulates
1.3 sulfide mineral segregations

economic importance

the economic importance of cumulate rocks best represented 3 classes of mineral deposits found in ultramafic mafic layered intrusions.

silicate mineral cumulates
oxide mineral cumulates
sulfide melt cumulates

silicate mineral cumulates

silicate minerals sufficiently valuable warrant extraction ore. however, anorthosite intrusions contain such pure anorthite concentrations mined feldspar, use in refractories, glassmaking , other sundry uses (toothpaste, cosmetics, etcetera).

oxide mineral cumulates

oxide mineral cumulates form in layered intrusions when fractional crystallisation has progressed enough allow crystallisation of oxide minerals invariably form of spinel. can happen due fractional enrichment of melt in iron, titanium or chromium.

these conditions created high-temperature fractionation of highly magnesian olivine or pyroxene, causes relative iron-enrichment in residual melt. when iron content of melt sufficiently high, magnetite or ilmenite crystallise and, due high density, form cumulate rocks. chromite formed during pyroxene fractionation @ low pressures, chromium rejected pyroxene crystals.

these oxide layers form laterally continuous deposits of rocks containing in excess of 50% oxide minerals. when oxide minerals exceed 90% of bulk of interval rock may classified according oxide mineral, example magnetitite, ilmenitite or chromitite. strictly speaking, these magnetite orthocumulate, ilmenite orthocumulate , chromite orthocumulates.

sulfide mineral segregations

sulfide mineral cumulates in layered intrusions important source of nickel, copper, platinum group elements , cobalt. deposits of mixed massive or mixed sulfide-silicate matrix of pentlandite, chalcopyrite, pyrrhotite and/or pyrite formed, cobaltite , platinum-tellurium sulfides. these deposits formed melt immiscibility between sulfide , silicate melts in sulfur-saturated magma.

they not strictly cumulate rock, sulfide not precipitated solid mineral, rather immiscible sulfide liquid. however, formed same processes , accumulate due high specific gravity, , can form laterally extensive sulfide reefs . sulfide minerals form interstitial matrix silicate cumulate.

sulfide mineral segregations can formed when magma attains sulfur saturation. in mafic , ultramafic rocks form economic ni, cu , pge deposits because these elements chalcophile , partitioned sulfide melt. in rare cases, felsic rocks become sulfur saturated , form sulfide segregations. in case, typical result disseminated form of sulfide mineral, mixture of pyrrhotite, pyrite , chalcopyrite, forming cu mineralisation. rare not unknown see cumulate sulfide rocks in granitic intrusions.